The present invention relates to a PCM (Pluse Coded Modulation) recording and reproducing apparatus for recording on and reproducing from a recording medium such as a magnetic tape, analog signals such as sound signals converted into digital signals.
Generally, in recording sound signals in form of digital signals in this type of a recording and reproducing apparatus, analog sound signals are first sampled with an optional sampling frequency Fs.
The sampling frequency Fs is determined on the basis of the reproducing frequency band. Theoretically, the sampling frequency Fs must be twice or more as high as the reproducing frequency band.
A higher sampling frequency is preferable in view of the reproduced sound quality, because the reproducing band width increases with the sampling frequency. On the other hand, however, the amount of data to be recorded also increases with the sampling frequency, and therefore, recording becomes more difficult as the sampling frequency increases.
In the conventional PCM recording and reproducing apparatus, the sampling frequency Fs for sound signals is, for example, 32 KHz, 44.1 KHz, 48 KHz, 50 KHz, 50.4 KHz etc. The sampling frequency Fs for the recording and reproducing apparatus must be set appropriately, taking into consideration the recording capacity of the recording and reproducing apparatus itself and the sampling frequencies of other equipment.
When a souce recorded digitally at a certain sampling frequency is to be input for recording in a digital form in a recorder of a different sampling frequency, the source must be subjected to D/A conversion to adjust the sampling frequency or the sampling frequency Fs must be changed by a frequency converter.
If a source recorded at a higher sampling frequency Fs is input to be recorded in a recorder of a lower sampling frequency, the sound quality will be deteriorated. Inversely, if a source recorded at a lower sampling frequency is input for recording in a recorder of a higher sampling frequency, the recording capacity of the recorder will not be effectively used. Accordingly, an ideal recording device should be capable of recording and reproducing a source at the same sampling frequency as that of the source, whatever the frequency it may have.
Various types of PCM recording and reproducing apparatus have been developed. Any of these types has a particular sampling frequency and therefore exhibits a number of problems in recording a digital source with another sampling frequency, though it has no problem in recording analog signals.